Most flights in UK airspace will be grounded until at least 7am tomorrow due to the cloud of volcanic ash that is moving south across the country, air traffic controllers said today.

Air travel remains badly disrupted in a dozen European countries, with 17,000 flights likely to be cancelled around the continent today.

The extent of the disruption, which has caused travel chaos for millions of passengers, remained hard to predict, the National Air Traffic Service (Nats) said in an update, describing the situation as "dynamic and subject to change".

The eruption of the Eyjafjallajokull volcano in south-east Iceland, which sent a plume of ash across some of the world's busiest flight paths, has brought the worst disruption to international air travel since September 11.

After monitoring the movement of the ash cloud, Nats said it would keep in place a block on commercial planes flying over England and Wales until 7am tomorrow.

From 7pm tonight, restrictions will be lifted over much of Scottish airspace, as well as Northern Ireland. While travel towards continental Europe remains affected, some trans-Atlantic flights will be allowed to resume, the Nats statement said, while warning travellers to check with airlines before leaving home.

It might be possible to ease restrictions at Newcastle airport after 1am tomorrow, the organisation added.

Civilian aircraft are not able to fly in Belgium, the Netherlands, Denmark, Sweden, Norway, Finland, Estonia, the north of France including all airports around Paris, parts of Germany including Düsseldorf, Cologne, Hamburg, Berlin and the airspace around Frankfurt, and parts of Poland including Warsaw airport.

Eurocontrol said: "Forecasts suggest that the cloud of volcanic ash is continuing to move east and south-east and that the impact will continue for at least the next 24 hours."

About 11,000 flights are likely to pass through European airspace today, compared with 28,000 on a normal day. Yesterday, there were 20,334 flights, Eurocontrol said.

Of the 300 or so transatlantic flights that would usually arrive at European airports in a day, between 100 and 120 were expected to touch down.

Airports around the UK were deserted, even though most staff arrived for work, with the airports operator BAA telling passengers to stay at home.

The ash cloud is seen as a significant danger to flights, particularly given its height, as the particles can cause engines to seize up. In 1982, a British Airways jumbo jet became a giant glider when all four of its engines failed after it flew through a volcanic plume over Indonesia. After a terrifying descent, the crew managed to get the engines started, before landing the plane safely in Jakarta.

Intermittent problems to air traffic could continue for six months if the eruption continued, one volcanologist said. The last time the volcano erupted in 1821, it spewed ash for two years.

The ash cloud, almost invisible to the eye, began to spread across Europe in the early hours of Wednesday before stretching east to northern Norway, Sweden and Finland and south across Scotland and the UK, engulfing Britain byyesterday afternoon.

The eruption of the volcano, which had been dormant for 187 years, caused devastation in Iceland. Civil protection teams evacuated about 700 residents when torrents of meltwater flowed off the glacier through fields and farms. Day turned to night east of the eruption as thick grey ash fell, leading to fears for grazing farm animals.

One UK airline has been flying as normal. Loch Lomond Seaplanes, which fly to Oban and Tobermory on Mull from Glasgow, travel below 5,000ft where the dust and clouds are not a problem.

David West, the company owner, said: "It's all about keeping out of the ash clouds and flying at low level. On the west coast yesterday we had very good visibility and no cloud."